Muir Glacier in 2007 is no longer a tidewater glacier; it has retreated. You see the term ‘retreated’ used often when speaking of vanishing glaciers. I don't like it much because I don't think it captures the gestalt of the process. Big valley glaciers don't move uphill, they can't go backwards as 'retreat' implies. What they do is melt. And they almost always melt faster at the lowest elevations. If they melt faster than they slide downhill, a series of photos or observations over time make it appear as if they have gone backward or retreated. Photographer: Bill Eichenlaub